Look through a microscope at a drop of pond water. One-celled amoebas or other microbes will quickly swim into view. Tiny as they may be, these organisms are massive, hulking giants compared to the building blocks of their bodies — single atoms and groups of atoms bonded together, called molecules.

Atoms and molecules dance inside every part of our world — from squirrels and clouds to peanut butter and bicycle tires. Such atomic jiggles and jumps play a major role in the chemical reactions and...